The feasibility of coupling laser light to individual microresonators is very significant with regard to using the microresonators as detectors. In Label-Free, Single-Molecule Detection with Optical Microcavities, Science 317, pp. 783-86, 2007, A. M. Armani, R. P. Kulkarni, S. E. Fraser, R. C. Flagan and K. J. Vahala describe the marker-free detection of single molecules that are applied to the surface of a microresonator. As a microresonator, a toroid is used which, in comparison to conventional resonator geometries, such as disks or spheres, has a quality factor (Q factor). The toroid is made of silicon dioxide (SiO2) and rests on a pedestal of silicon (Si) that is disposed on a substrate that is likewise composed of Si.
In Ultra-high-Q toroid microcavity on a chip, Nature 421, pp. 925-28, 2003, D. K. Armani, T. J. Kippenberg, S. M. Spillane and K. J. Vahala describe the coupling of laser light to individual microresonators through thinned glass fibers. However, this entails considerable difficulty when coupling is performed to more than two microresonators. The reason for this is the thinned region of the glass fibers that is used for the coupling. The small diameter of the glass fiber (approximately 1-2 μm) makes it very sensitive to mechanical stress, and the thinned region is not completely straight due to the fabrication process. Thus, it is difficult to orient the thinned region of the glass fiber in parallel to the substrate without making contact with the substrate. Moreover, the glass fiber degrades within two to three days.
In Silica on Si waveguides for self-aligned fibre array coupling using flip-chip Si V-groove technique, Electronics Letters 32, pp. 1916-1917, 1996, Q. Lai, W. Hunziker and H. Melchior present what is generally referred to as the flip-chip principle for the butt-coupling of a glass fiber to waveguides.
In Long-period gratings in polymer ridge waveguides, Optics Express 13, pp. 1150-60, 2005, Q. Liu, K. S. Chiang and K. P. Lor describe the advantages of polymer ridge waveguides over ridge waveguides of glass or of crystals such as lithium niobate (LiNbO3) or silicon.
In Design and Applications of Optical Microsphere Resonators, Dissertation, Helsinki University of Technology, pp. 20-21, 2003, J. Laine schematically describes bringing a first substrate, which contains a waveguide, into proximity of two microspheres that have been placed on a second substrate, based on the flip-chip principle. There is no discussion of the relative positioning of the two substrates.